1. Field of the Invention
The present invention relates to a method of lithography and, in particular, a method of lithography in which an optimal process condition can be selected simply and precisely.
2. Description of the Related Art
Recently, in line with an increasingly fine patterned structuring of electronic devices due to advancements on very large scale integration and multifunctional characteristics in semiconductor devices, various types of lithographic technology have been developed. For example, in a lithographic method using an ArF excimer laser beam or an electron beam as its exposure beam, a process using a chemically amplified resist is now becoming a mainstream.
In these lithographic methods using the chemically amplified resist, there are essential conditions required when forming a high precision resist pattern such as a pre-bake (hereinafter referred to simply as PB) condition necessary after coating of a resist, a post exposure bake (hereinafter referred to simply as PEB) condition necessary after exposure of the resist, and optimization of developing conditions necessary after PEB or the like.
As a result, when performing lithographic processing, these process conditions are optimized through bench tests or evaluation experiments on each process condition and by selection of optimal values thereof at which an optimized resolution is obtained.
However, these optimal values necessary for the above-mentioned process conditions vary depending on various process parameters, such as the patterning area (an area of exposure), the film thickness of its resist and the like. As a result, in order to optimize these process conditions, it becomes necessary to carry out a respective evaluation experiment or a bench test for each of these process parameters, thereby requiring substantial time and labor.
The present invention has been conceived in order to solve the problems associated with the conventional process and to provide a novel method of lithography that enables the optimization of the process conditions simply and precisely upon a reduced number of experiments required therefor.
According to the present invention, in order to solve the above-mentioned problem, a resist pattern is formed on the basis of an orthogonal experiment that is carried out by varying each process condition, and a line edge roughness of such formed resist pattern is obtained as a characteristic value for evaluation. Then, a value at a respective reference (benchmark) level set for each factor in the orthogonal experiments and at which value the edge roughness becomes minimal is selected for its lithographic process. Further, the orthogonal experiment is carried out on the basis of an orthogonal table therefor.
According to such method of lithography of the present invention, the orthogonal experiment having a high reproducibility therefore has a satisfactory high reproducibility, a change in its process conditions is reflected with high sensitivity, and an edge roughness having a linear correlation relative to the resolution of the patterning is used as a characteristic value for evaluation. Therefore, an optimal process condition including respective factors for an improved resolution can be selected more precisely and at high reproducibility by reflecting a specific effect of each process condition or factor on the resolution. Further, because of the fact that the orthogonal experiment is conducted based on the orthogonal table, a result of experiments having high reproducibility can be obtained with a substantially reduced number of experiments.
In other words, the method of lithography according to the present invention described hereinabove enables advantageously the reflection of an influence of change in each process condition over the resolution of the resist patterning more precisely and with an improved reproducibility, so that an optimal process condition that allows the resolution to become maximum can be selected simply and precisely, thereby ensuring a higher precision resist pattern to be formed. In addition, the experiments conducted based on the orthogonal tables of the invention ensure that an appropriate process condition will select more simply and with a reduced number of experiments.